1. Field of the Invention
The present invention relates to an improved torque wrench for fastening or unfastening screws such as a bolt or a nut.
2. Description of the Related Art
A widely used hand wrench has a handle, a ratchet mechanism housed in the head of the handle, and an output shaft rotatably disposed at the head. By turning the handle clockwise and counterclockwise in a reciprocating manner, the ratchet mechanism allows the output shaft to rotate in one direction and thus a socket attached to the output shaft to fasten or unfasten a screw.
In order to construct a torque wrench utilizing such a hand wrench, the handle is formed of a sheath tube 31, as shown in FIG. 9.
The sheath tube 31 is pivotally attached to the base of a head 32 at the front thereof. The sheath tube 31 has a pestle 33 extending backwards from the head 32 inserted thereinto. Also, the sheath tube 31 has a slider 34 disposed in the central part thereof. The slider 34 and the pestle 33 oppose each other at the slanted opposing surfaces thereof and are connected by a link toggle 35 disposed orthogonal to these opposing surfaces.
In addition, the sheath tube 31 has a torque adjusting screw 36 and a nut 37, which is screwed together with the torque adjusting screw 36, disposed in the rear part thereof. Furthermore, the sheath tube 31 has a coil spring 38 placed between the nut 37 and the slider 34.
The head 32 has an output shaft 39 rotatably disposed in the center thereof.
In order to fasten a screw by using the torque wrench having the above-described structure, the sheath tube 31 is turned clockwise and counterclockwise in a reciprocating manner.
With this arrangement, by turning the output shaft 39 via the ratchet mechanism in its fastening direction, the torque wrench fastens a screw inserted in a socket attached to the output shaft 39.
After the screw is placed at the predetermined position thereof, and when the fastening torque reaches a predetermined value by further turning the sheath tube 31 clockwise and counterclockwise, the link toggle 35 is activated and then the pestle 33 and the slider 34 hit against each other at the opposing surfaces thereof. A hitting sound caused by the above hitting or a turning lash of the sheath tube 31 allows an operator to determine if the torque wrench reaches a predetermined fastening torque of the screw.
A power torque wrench in which a motor for transmitting a rotating torque to the output shaft 39 is incorporated into the foregoing structure of the hand torque wrench is considered. However, when the motor is disposed in the rear part of the sheath tube 31, the pestle 33 extending from the head 32, the slider 34, and so forth disposed in the central part of the sheath tube 31 hinder the power torque wrench to have a structure in which the torque of the motor is transmitted to the output shaft 39.
To solve this problem, as disclosed in Japanese Patent Application Publication No. 8-112775 and also as shown in FIG. 10, another power torque wrench is constructed such that the sheath tube 31 has a motor 40 disposed above the front half thereof so that the torque of the motor 40 is transmitted to the output shaft 39.
With this structure, in the fastening operation of this torque wrench, the motor 40 rotates the output shaft 39 at high speed so as to place a screw at the predetermined position thereof. After the screw is placed, the sheath tube 31 is turned by hand up to a predetermined fastening torque in a similar fashion to that of the hand torque wrench.
In the foregoing power torque wrench, the motor 40 is additionally attached above the sheath tube 31. Accordingly, the enlarged height of the whole torque wrench not only makes the handling of the torque wrench difficult but also may cause a problem in that, when a working space is tight or there is an obstruction around an object to be fastened, the motor 40 hinders an operator to perform his or her fastening work. Also, the torque wrench becomes unstable because of the center of gravity of the torque wrench is shifted upwards by the motor 40, thereby resulting in the poor operationality thereof.
In view of the above problems, the present invention has been made. Accordingly, it is an object of the present invention to provide a torque wrench which has a motor, which is housed therein but not additionally attached thereon, so as to make the whole size thereof compact, achieves improved handling and operationality, smoothly transmits the torque of the motor to an output shaft, and also allows an operator to fasten a screw with a predetermined fastening torque by hand.
A torque wrench according to the present invention comprises a motor; an output shaft; a straight hollow handle comprising a grip, housing the motor therein, integrally formed therewith at the rear thereof; a head disposed at the front of the hollow handle and rotatably supporting the output shaft in the vertical direction so as to be orthogonal to the longitudinal direction of the hollow handle; a transmission shaft disposed in the hollow handle; a rotation-direction changeover mechanism which transmits the rotation of the motor to the output shaft via the transmission shaft; a sheath tube which covers the front half of the hollow handle with a predetermined gap between the inner surface of the sheath tube and the outer surface of the hollow handle, and which is connected to the head at the front thereof and to the front of the hollow handle; a slider moveably disposed around the hollow handle in the longitudinal direction of the hollow handle such that the front end surface of the slider opposes the rear end surface of the sheath tube; a torque transmitting mechanism disposed between the mutually opposing end surfaces of the slider and the sheath tube; and a torque adjusting mechanism disposed in the rear of the slider and around the rear half of the hollow handle.
With this structure, although the hollow handle is formed so as to be independent from the head rotatably supporting the output shaft, the torque of the motor housed in the grip at the end of the hollow handle is reliably transmitted to the output shaft via the transmission shaft in the hollow handle, and also a screw can be fasted by hand.
Accordingly, since the whole structure of the torque wrench becomes compact, the torque wrench can be easily handled and stably operated so that a screw is smoothly fastened even when a working space is tight or there is an obstruction around the screw.
In addition, by rotating the motor when the rotation-direction changeover mechanism is changed over to a fastening mode of a screw, the output shaft is quickly rotated only in the fastening direction of the screw so that the screw is quickly fastened to the seating surface thereof.
When the screw is seated on the seating surface, by turning the hollow handle by hand clockwise and counterclockwise in a reciprocating manner, the torque of the manual turning operation is transmitted to the sheath tube via the torque transmitting mechanism. Then, the sheath tube turns about the output shaft in a reciprocating manner so that the screw is further fastened via the rotation-direction changeover mechanism only when the sheath tube turns outwards.
Furthermore, when the frictional force between the screw and the seating surface reaches a value corresponding to the predetermined fastening torque set by the torque adjusting mechanism, the torque transmitting mechanism is activated so as to reliably determine that the screw has been fastened with the predetermined fastening torque.
In the torque wrench according to the present invention, the rotation-direction changeover mechanism is preferably characterized in that the head has a center hole vertically extending therethrough, the output shaft is formed as a regular polygonal column extending in the vertical direction and having side surfaces, and rotatably disposed in the center hole of the head, a space is formed between each side surface of the output shaft and the inner wall of the center hole, and divided into a pair of wedge-shape spaces, each becoming narrower from the center to the corresponding edge of the side surface, a cylindrical locking member is disposed in the middle of the space so as to engage into either one of the wedge-shape spaces on both sides thereof, and a changeover member, which pushes the locking member toward either one of the wedge-shape spaces on both sides thereof, is disposed in a space between the adjacent cylindrical locking members so as to be moveable for changeover in the circumferential direction of the output shaft.
With this structure, by turning the head about the output shaft in the fastening direction of the screw, the locking members engage into the corresponding wedge-shape spaces ahead of the fastening direction, whereby the turning torque of the head is reliably transmitted to the output shaft.
Also, when the head is turned in the unfastening direction of the screw, the locking members disengage from the corresponding wedge-shape spaces and are received by the corresponding changeover pieces within the moveable regions of the corresponding spaces. Accordingly, the screw can be fastened by transmitting the fastening torque of the head to the output shaft only when the head is turned in the fastening direction of the screw by a predetermined angle.
In the torque wrench according to the present invention, the torque transmitting mechanism may comprise a pair of first projections disposed at the upper and lower parts of the rear periphery of the sheath tube and having slanted engaging surfaces protruding toward the rear direction.
In addition, the torque transmitting mechanism may comprise a pair of second projections disposed at the upper and lower parts of the front periphery of the slider and disengageably engaging the corresponding slanted engaging surfaces of the first projections.
With the structure, when the hollow handle is turned to fasten the screw by hand, since the first and second projections are engaged with each other, the turning torque of the manual operation is reliably transmitted to the sheath tube so as turn the output shaft.
When the fastening torque of the screw reaches a predetermined value, since the second projections close to the hollow handle move in the fastening direction of the screw relative to the corresponding first projections close to the sheath tube, the fact that the screw has been fastened with the predetermined fastening torque is easily confirmed.
In the torque wrench according to the present invention, the torque adjusting mechanism may comprise an adjusting nut which is screwed together with a male-threaded portion formed on the rear half of the hollow handle and an adjusting coil spring disposed between the mutually opposing end surfaces of the adjusting nut and the slider in a compressed manner.
With this structure, by moving the adjusting nut disposed around the hollow handle in the back and forth direction, since the engaging force between the first and second projections can be easily varied, the fastening torque of the screw can be precisely adjusted so as to be a predetermined fastening torque.
When the motor housed in the grip of the hollow handle is turned when the grip is held and the rotation-direction changeover mechanism is changed over to the fastening mode of the screw, the rotation of the motor is transmitted to the output shaft disposed in the head via the transmission shaft disposed in the hollow handle, and the rotation of the output shaft causes the screw to turn in the fastening direction thereof.
When the screw is seated on the seating surface, since the frictional force between the screw and the seating surface increases and becomes greater than a value corresponding to the torque of the motor, the torque of the motor becomes insufficient and the screw cannot be further fastened until the fastening torque of the screw reaches a predetermined value. Accordingly, the screw is further fastened by hand so that the fastening torque of the screw reaches the predetermined value.
The manual fastening operation is performed by operating the grip so as to turn the hollow handle clockwise and counterclockwise in a reciprocating manner. By turning the hollow handle in a reciprocating manner, the sheath tube turns about the output shaft in a reciprocating manner via the torque transmitting mechanism, thereby allowing the screw to be fastened via the rotation-direction changeover mechanism when the sheath tube moves outwards.
When the frictional force between the screw and the seating surface increases to a value corresponding to the fastening torque set by the torque adjusting mechanism, the torque transmitting mechanism is activated. With this activation, an operator is informed by his or her hand holding the grip that the fastening torque of the screw has reached a predetermined value. Then, the operator stops handling the hollow handle and finishes fastening the screw by hand.
When the fastened screw is to be unfastened, the rotation-direction changeover mechanism is changed over to an unfastening mode of the screw. By turning the hollow handle counterclockwise, the unfastening turning torque of the hollow handle is transmitted to the output shaft so as to reduce the frictional force between the screw and the seating surface. Subsequently, by turning the motor housed in the grip, the rotation of the motor is transmitted to the output shaft in an unfastening-direction via the transmission shaft disposed in the hollow handle and also via the rotation-direction changeover mechanism so that the screw is quickly unfastened.
Although the above description deals with a right-hand screw, those skilled in the art will appreciate that the present invention is applicable to a left-hand screw.